Stacked SPAD Junction Structure for Wider Operating Voltage Range
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Solution Overview
Problem
Conventional single photon avalanche diodes (SPADs) have limited operational voltages, which restrict their sensitivity and application in various environments, making them less effective for accurate time-of-flight measurements.
Innovation Solution
The design of a single photon avalanche diode with multiple depletion regions and distinct breakdown voltages, achieved through vertically stacked P-N junction diodes and isolation regions, allowing for multiple operational voltages and enhanced detection sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional single photon avalanche diode with a single depletion region is used, then the device structure is simple, but the operational voltage range is limited and detection sensitivity is restricted
Solution Approach 1:
The single depletion region is segmented into multiple depletion regions with different breakdown voltages. Each depletion region is formed by a separate P-N junction diode stacked vertically, allowing the device to operate at multiple voltage levels (first operational voltage, second operational voltage, etc.) corresponding to different detection depths and sensitivities.
Solution Approach 2:
The patent transitions from a single-layer depletion region to a vertically stacked multi-layer structure. By adding the depth dimension through multiple depletion regions at different vertical positions (first depth, second depth, third depth), the device gains the ability to detect photons from different depths and operate at multiple voltages simultaneously.
2Measurement precision
If multiple depletion regions with different breakdown voltages are implemented, then detection sensitivity in various environments is improved, but the device structure becomes more complex
Solution Approach 1:
Each depletion region is designed with specific local characteristics including different breakdown voltages, different vertical depths, and different spatial positions. The first depletion region operates at a first breakdown voltage for shallow detection, while the second and third depletion regions operate at higher breakdown voltages for deeper detection, allowing optimized sensitivity for different detection requirements.
Solution Approach 2:
The multi-depletion region structure enables the single photon avalanche diode to perform multiple detection functions within a single device. It can detect photons at different depths, operate at multiple voltage levels, and adapt to various environmental conditions, making it universally applicable for different time-of-flight measurement scenarios.
3Adaptability or versatility
If vertically stacked P-N junction diodes are used to create multiple depletion regions, then multi operational voltages are achieved, but manufacturing complexity increases
Solution Approach 1:
The fabrication process is segmented into distinct stages for forming each P-N junction diode and its corresponding depletion region. Isolation regions are introduced between the stacked diodes to electrically separate them, allowing independent control and formation of each junction during the CMOS fabrication process.
Solution Approach 2:
The P-N junction diodes are nested vertically within the CMOS substrate, with each subsequent diode built upon the previous one. The isolation regions are nested between the diodes to provide electrical separation, creating a compact multi-functional structure that can be integrated into standard CMOS fabrication flows.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This multi-depletion region structure improves the detection sensitivity and expands the application fields of the SPAD, enabling effective time-of-flight measurements across various environments.
Implementation Method 1
A single photon avalanche diode may include a first diode, a second diode and a third diode... The first diode includes a first PN junction vertically spaced from a light-receiving surface...
Implementation Method 2
single photon avalanche diode... different breakdown voltages from one another... multi operational voltages corresponding to numbers of the multi-depletion regions
Data Source
AI summary
A single photon avalanche diode may include a first diode, a second diode and a third diode. The first diode includes a first PN junction vertically spaced from a light-receiving surface by a first depth. The second diode is in partial contact with the first diode. The second diode includes a second PN junction vertically spaced from the light-receiving surface by a second depth greater than the first depth. The third diode is in partial contact with the second diode. The third diode includes a third PN junction spaced from the light-receiving surface by a third depth greater than the second depth. The first to third diodes have different breakdown voltages from one another.